Prior to the invention, a manual gauging operation was performed in order to detect surface profile defects such as thin rim, high flange and thin flange profiles on the steel wheels of rail cars. This manual gauging was done using hand instruments and templates in accordance with standards and procedures set forth in the Association of American Railroads Wheel and Axle Manual (Section G, Part II) as well as the Field Interchange Manual. However, manual wheel gauging was extremely slow, labor intensive, and highly subjective. Furthermore, it could not be performed while the wheel was in motion.
Attempts at automating wheel inspection in the railroad industry include a high flange detection device disclosed in U.S. Pat. No. 4,076,192, and a wheel flange inspection device marketed by Wheel Checkers Ltd. of Denver, Colorado, USA, under the trade name WHEEL CHECKER. These devices mechanically detect a flange profile defect by relying on a defective flange to contact a gauging surface which actuates an alarm when contact is made. However, these devices have proven unsatisfactory due to their mechanical nature, their inability to detect profile defects other than on the flange of the wheel, and their difficulty in upgrading associated signal methods.
A further attempt at automating wheel inspection includes a wheel profiling system recently introduced by Hegenscheidt Corporation. This system utilizes laser optics to effect non-surface contact profiling of in-motion wheels. However, this system has been evaluated and determined to be an unsatisfactory approach for automated detection of wheel profile defects because it uses light sensitive optics which are unreliable in the dirty and rough service environments typical of North American heavy freight railroad operations. All-weather protection as well as ambient light exclusion would be essential for effective operation of this system. Accordingly, the construction of pull-through sheds of approximately two to three car lengths in size would be necessary to accommodate the system. Further disadvantages include difficulty in using the system at locations isolated from terminal points, inability to group individual profiler installations into multi-unit networks controlled by a centralized computer, and extremely high purchase costs associated with the system.